So I was surprised when I started reading that one character supposedly has aphasia, a language condition that affected me during and after my stroke, and many, many others. Maybe even you.
Now, aphasia does NOT diminish one's intelligence. You've got all those thoughts in there, and aphasia is often a barrier to get those thoughts out through speech.
So I did a little research, and instead of this being an instance to educate the public about aphasia, the talk that the character Hodor has aphasia - which is incorrect - has bolstered the mistaken impression that aphasia effects intelligence. Again, it does not.
Here's a good rundown on why this idea is wrong, highlighting that Hodor does not have aphasia:
Communication disorders can present in subtle but heartbreaking ways, and aphasia is no exception. Communication is separate from cognition, but if you can't verbally explain to people what you know, your intellect is nonexistent. Uninformed listeners are quick to assume that you are stupid, foolish, or ignorant if you can't communicate in a "normal" fashion. If you can't say it, you don't know it.
This is why it is so dangerous to blithely Wikipedia-diagnose Hodor with aphasia. Hodor does have a communication disorder, but it is vastly different in cause and effect than true, pure aphasia. (Cognitive brain damage can certainly co-occur with aphasia in cases of neurologic trauma or dementia, but they are two separate diagnoses.)
If someone who had never heard of aphasia was to take the original article at face value, it would be reasonable for them to assume that people with aphasia have the intellectual ability of a 3-year-old. It's difficult enough to be suddenly robbed of your eloquence as an adult, and now everyone assumes you have an IQ of 50, to boot? "Just like that guy on Game of Thrones!"